DE 10 2009 024 026 A1 provides a control valve for a camshaft adjuster, including a hollow cylindrical control piston that is displaceably guided within a valve housing. A hydraulic double check valve which unblocks a first pressure medium line in the inflow direction, and which includes a closing part having a sealing surface, and via which the inflow opening is closable in the return direction, is situated within the piston cavity. The pressure medium arrives at one of control connections A or B via the inflow connection and the piston cavity. The discharge of the pressure medium from control connection A or B takes place via one of the two outflow connections, each associated with one of the control connections. The outflowing pressure medium is conducted via the outflow connection of the control valve into the cylinder head or the chain case.